When I do this UV unwrap the cube becomes transparent and shows vertical and horizontal lines
The lines are most likely a problem with the image Alpha channel. However, the Blend file you uploaded does not include the image - you need to select 'Pack' in the UV editor to pack the image into the file before you upload it. However, load the image into an image editor and check the Alpha channel to ensure there are no lines or other noise present. Also, set the Image Texture node to 'Clip' rather than 'Repeat' - this way the other 5 UV faces (outside the UV boundary in your image) definitely won't be picking up any content from the image.

As for the cube becoming transparent, you do realise that you're using a Transparent shader for the red shading...? Replace the Transparent shader node with a Diffuse shader node and it will no longer be transparent.